Cellular wireless is an increasingly popular means of personal communication in the modern world. A cellular wireless network may include a plurality of base transceiver stations (BTSs), each BTS providing a respective coverage area. Generally, when a mobile station is positioned within a coverage area of a BTS, the mobile station can communicate over an air interface with the BTS, and in turn over one or more circuit-switched and/or packet-switched signaling and/or transport networks to which the BTS provides access.
The coverage area of a BTS is sometimes referred to as a cell. A given cell may be divided geographically into a number of sectors (which can be visualized ideally as pie pieces), with each sector being defined respectively by radiation patterns from directional antenna components of the respective BTS, or by respective BTS antennae. In operation, a BTS typically emits a pilot signal on each sector, and a mobile station in receipt of a pilot signal constantly measures the strength (Ec/Io, i.e., energy versus spectral density) of the pilot and notifies the cellular wireless network when the signal strength of the pilot falls above or below designated thresholds.
The cellular wireless network providing service to the mobile station usually stores a “neighbor list” (or “macro-network neighbor list”) of the one or more sectors currently serving the mobile station. In particular, the neighbor list typically includes sectors in the cellular wireless network that are not in the mobile station's active set (i.e., the one or more sectors currently serving the mobile station), but are nonetheless in close proximity to the one or more sectors serving the mobile station.
Further, a mobile station may maintain in its memory, in addition to the neighbor list, a list of the sectors in its active set and a list of “candidate” sectors, the candidate sectors including sectors that are not yet in the active set but that have sufficient signal strength such that the mobile station could demodulate signals from those sectors. All other possible sectors are members of a “remaining” set. During operation, if a pilot signal from a given sector in the neighbor list is above a threshold pilot-signal strength, then the mobile station may notify the cellular wireless network to this fact, and the cellular wireless network may responsively enable the mobile station to hand off to the given sector.
BTSs of the above-described cellular wireless network are typically not associated with any subscriber or small group of subscribers in particular; rather, they are placed in publicly-accessible locations and are used by the service provider's customers generally. These BTSs collectively blanket cities, rural areas, etc. with coverage; as such, they are referred to generally and herein as “macro BTSs” or “macro-network BTSs.” The coverage area associated with a given macro BTS may be referred to as a “macro coverage area,” and the macro coverage area may be associated with a “macro cell” and/or divided into “macro sectors.” Further, the cellular wireless network to which a macro BTS belongs may be referred to as a “macro network.”
To address gaps in macro-network coverage (e.g., in buildings) and for other reasons, macro-network service providers have recently begun offering consumers devices referred to herein as femto cells, which may also be referred to as femto base stations, femto BTSs, picocells, pico base stations, pico BTSs, microcells, micro base stations, micro BTSs, private base stations, private BTSs, low cost Internet base stations (LCIBs), and by other names. Note that the aforementioned terms that end in “cell” may also be generally and herein used interchangeably to refer to the coverage area provided by the respective device. Hence, the term “femto cell” may be used interchangeably with the term “femto coverage area.”
A typical femto cell may be approximately the size of a desktop phone or WiFi access point, and may be characterized as a low-power, low-capacity version of a macro base station. Femto cells are typically located in a person's home or office, as examples.
The femto cell may have a wired (e.g. Ethernet) or wireless (e.g. WiFi) connection with the user's router, and would thus have connectivity to the Internet and/or one or more other packet-data networks via the user's broadband connection. A femto cell may establish a virtual-private-network (VPN) connection over the Internet with an entity (e.g. a VPN terminator) on the wireless-service (macro-network) provider's core network, and thereby be able to securely communicate with the VPN terminator and other entities on that core network and beyond.
The femto cell may also have a wireless-communication (e.g. CDMA) interface that is compatible with a user's mobile station(s), such that the femto cell may act as a micro base station, providing coverage on the wireless-service provider's network via the user's Internet connection. Usually, a femto cell will provide service on a single RF carrier (or on a single carrier per technology, where multiple technologies (e.g., CDMA, EV-DO) are supported), and also transmit a pilot signal that identifies the femto cell.